This invention relates to the electrical measurement art, and more particularly to a new and improved sensor or probe for use on an electrostatic field or electrostatic voltage measuring device.
A device which measures electrostatic fields or electrostatic potential on sufaces without current flow through the device, either capacitive or resistive current, is known as an electrostatic voltmeter. These devices comprise a probe or sensor assembly and an associated voltmeter assembly. The sensor, functioning as an electrostatic detector, is capacitively coupled to the field or surface to be measured, in a non-contacting manner. The voltmeter assembly receives data from the sensor and produces a high quality output signal which is used to drive an indicator or used to control an electrostatic process related to the measurement or both.
Recently it has been determined that the electrostatic processes involved in the electrophotographic process, as used for example in an office copy machine or in a high speed electrostatic printing process, could be greatly enhanced to produce better quality reproductions under conditions of varying ambient conditions, such as humidity changes, temperature changes, or changes in the characteristics of the photoreceptor due to age or use, if the photoreceptor surface voltage is measured during the process. The measurement of the photoreceptor voltage and the production of a signal representative of that voltage would allow for automatic adjustment of the machine process thus producing better quality reproductions with fewer machine adjustments and service.
Heretofore, electrostatic sensors of the type required to produce accurate measurements of photoreceptor surface voltage in the harsh machine environments of high toner contamination, varying humidity and temperature conditions and restricted space availability have not been available. Additionally, the cost of currently available sensors would preclude their use in these machine applications because of their complex nature and high manufacturing costs.